High Capacity Electrodes

ABSTRACT

A high capacity electrode includes a conducting substrate on which a plurality of support filaments are disposed. Each of the support filaments have a length substantially greater than their width and may include, for example, a carbon nano-tube (CNT), a carbon nano-fiber (CNF), and/or a nano-wire (NW). The support filaments are coated with a material, such as silicon, having a greater ion absorbing capacity greater than the neat support filaments. A trunk region of the support filaments proximate to the substrate is optionally kept free of ion absorbing material. This trunk region allows for the expansion of the ion absorbing material without detaching the support filaments form the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/392,525 filed Feb. 25, 2009 and also entitled “High CapacityElectrodes” which claims priority of and benefit to U.S. ProvisionalPatent Applications 61/067,018 filed Feb. 25, 2008 and 61/130,679 filedJun. 2, 2008. The disclosures of the above applications are herebyincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The invention is in the field of battery technology.

2. Related Art

Four basic design parameters of a battery/fuel cell (battery) includeenergy density, power density, cycle life, and safety. Energy densityrefers to how much energy the battery can store, measured in units ofmega-joules/kilogram (MJ/kg.) Power density (also referred to aspower-to-weight ratio and specific power) refers to how quickly thestored energy per unit mass can be delivered, and is measured in unitsof kilowatts/kilogram (W/kg). Cycle life refers to the charge capacityof the battery vs. the number of charge/discharge cycles. Typically, alarger cycle life is more useful. Safety considerations for a batteryinclude processes that could harm person or property, for example, toxicchemical release and overheating to the point of fire.

FIG. 1 illustrates a cross section of a prior art lithium-ion secondary(rechargeable) battery/cell 100. The secondary battery/cell 100 includesan anode 120, an electrolyte 140, a separator 130, an electrolyte 140,and a cathode 110. In some cases, the anode 120 includes graphite.Reasons for using graphite for the anode 120 include relative ease ofLi-ion intercalation and low cost of graphite. Alternatively, the anode120 includes silicon applied directly to the bulk (macroscopic)substrate of the anode. A reason for using silicon is that silicon canintercalate roughly ten times more Li-ions than graphite. Unfortunately,silicon typically expands 400% or more upon full Li-ion intercalation,which can cause silicon breakage and substantially compromise adhesionof silicon to the anode 120, thus, decreasing longevity.

The separator 130 between the secondary battery/cell 100 includes aporous membrane. In some embodiments, the porous membrane is amicroporous polyolefin membrane. Microporous polyolefin does notparticipate in the reactions inside the battery. The separator 130 istypically about 50 microns thick and includes pores 135. A typicalaverage of the size of the pores 135 is about of 2.0 microns or more.

The cathode 110 of the secondary battery/cell 100 is generally of threetypes. These three types include a layered oxide (such as LiCoO₂,LiMnO₂, or LiNiO₂), a polyanion (such as lithium iron phosphate), or aspinel (such as manganese oxide). The material used for the cathode 110is typically a bulk material or a bulk deposited/grown film.Unfortunately, due to the macroscopic nature of these materials, iondiffusion in the bulk material of the cathode 110 limits the oxidationand reduction rates during the charge and discharge cycles. The poordiffusion rates of the ions limits the overall power density. Thecathode may be electrically coupled to an electrical contact point 150Afor drawing current from the battery/cell 100. The anode may beelectrically coupled to an electrical contact point 150B for drawingcurrent from the battery/cell 100.

The electrolyte 140 in the secondary battery/cell 100 may be a saltdissolved in a solvent, such as LiClO₄, LiPF₆, LiBF₄, and/or the like.

SUMMARY

Various embodiments of the invention include a system comprising anelectrode disposed in a first region of electrolyte and including asubstrate, a plurality of support filaments attached to the substrate,and an ion absorbing material attached to the support filaments andconfigured to expand in volume at least 5 percent when absorbing ions; aseparator configured to separate the first region and a second region ofelectrolyte; and a cathode disposed in the second region of electrolyte,the cathode, anode and separator configured to operate as a rechargeablebattery.

Various embodiments of the invention include an electrode comprising aconductive substrate; a plurality of support filaments attached to thesubstrate, the support filaments comprising a carbon nano-tube (CNT), acarbon nano-fiber (CNF), or a nano-wire (NW), and an ion absorbingmaterial attached to some but not all of each of the support filamentsand configured to expand in volume by at least five time when absorbingions.

Various embodiments of the invention include a method comprisingreceiving a conductive substrate; forming a plurality of supportfilaments coupled to the conductive substrate, the support filamentshaving an aspect ratio (length/width) of at least 10:1; and coating theplurality of support filaments with an ion absorbing material to createan electrode, the ion absorbing material having at least a ten timesgreater ion absorbing capacity for ions than the support filaments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a prior art rechargeable battery.

FIG. 2A illustrates a cross section of an electrode, according tovarious embodiments of the invention.

FIG. 2B is a cross section illustrating details of a seed layer of FIG.2A according to various embodiments of the invention.

FIG. 2C is a cross section of a portion of the electrode extension ofFIG. 2A illustrating an under-layer between a support filament and anintercalation layer, and an over-layer that encapsulates theintercalation layer, according to various embodiments of the invention.

FIG. 3 is a cross section of the electrode of FIG. 2 illustratingdetails of a support filament of FIG. 2A, according to variousembodiments of the invention.

FIG. 4A illustrates a cross section of an alternative electrode,according to various embodiments of the invention.

FIG. 4B illustrates a cross section of an alternative electrode,according to various embodiments of the invention.

FIG. 4C is a cross section illustrating details of a support filament ofFIG. 4A, according to various embodiments of the invention.

FIG. 5A illustrates a cross section of an alternative electrode,according to various embodiments of the invention.

FIG. 5B illustrates details of support filaments and of the electrode ofFIG. 5A, according to various embodiments of the invention.

FIG. 6A illustrates a cross section of an electrode extension of FIG. 2Ataken along line a-a, according to various embodiments of the invention.

FIG. 6B illustrates a cross section of a support filament of FIG. 2Ataken along line a-a, according to various embodiments of the invention.

FIG. 6C illustrates a cross section of the support filament of FIG. 2Ataken along line a-a, according to various embodiments of the invention.

FIG. 7 illustrates further embodiments of a support filament, accordingto various embodiments of the invention.

FIG. 8 illustrates methods of producing and optionally using anelectrode, according to various embodiments of the invention.

DETAILED DESCRIPTION

Various embodiments of the invention include a rechargeable (secondary)battery including an improved electrode. The electrode of the inventionis optionally included within a part of a cathode and/or an anode of asecondary battery/cell 100 to create an improved battery. The electrodetypically includes an electrode extension grown on or attached to asubstrate using a seed layer. The electrode extension is configured toincrease the surface area of the electrode and includes a supportfilament and an intercalation layer. In various embodiments, the supportfilament material includes a carbon nano-tube (CNT), a carbon nano-fiber(CNF), a nano-wire NW (a wire having a diameter less than approximatelyfive micrometer), metal, semiconductor, insulator, silicon, and/or thelike. The CNT, CNF, and/or NW may be single walled or multi walled. Thesupport filament may provide an electrical path to the substrate and amechanical base for the intercalation layer. The intercalation layerprovides a region for absorption and/or donation of ions from theelectrolyte. As used herein, an intercalation layer can be used at bothan anode and a cathode. In various embodiments, the intercalation layerincludes a donor/acceptor material (DAM) configured for donating and/oraccepting the ions from the electrolyte. This ion donating and/oraccepting may include both adsorbing and absorbing processes. Theintercalation layer may expand in volume by at least 5, 10, 15, 50, 100,200 or 400 percent on the absorption of ions.

In various embodiments, the DAM includes silicon, graphite, Sn, Sn—C,inter-metallics, phosphides, nitrides, 3D metal oxides, or LiCoPO₄,LiMnPO₄, LiMn₂O₄, LiCoO₂, LiNiO₂, MnO₂, vanadium oxides V₂O₅ and LiV₃O₈,polyanionic materials such as Li(1-x)VOPO₄, Li(x)FePO₄), LiMnO₂,Li₂FePO₄F, doped LiMn₂O₄, and/or the like. The DAM is deposited or grownon the support filament. In some embodiments, the support filament isprovided with additional strength (e.g., tensile, compression, shear,and/or the like) for supporting the DAM particularly during expansionand/or contraction of the DAM in the intercalation layer. In someembodiments, the DAM covers part but not all of the support filament.For example, portion of the support filament may remain uncoated. Theuncoated portion can provide for flexibility and freedom of movement,for example between the electrode extension and the substrate. In somecircumstances this reduces the likelihood of separation of the supportfilament from the seed layer during expansion and/or contraction of theDAM in the intercalation layer.

The electrode extension increase intercalation volume and surface area,thereby improving energy density of the electrode over a layer ofmaterial deposited on a flat surface. The electrode extensions may serveas a flexible interface between the substrate and intercalation layer,thereby allowing a large degree of expansion in volume (e.g., 2×, 4×,6×, etc.) of the intercalation layer, while at the same time reducing arisk of the material separating from the substrate. The electrodeextension can also reduce diffusion distances of the ions in the bulk ofthe intercalation material, therefore improving power density of theelectrode.

FIG. 2A illustrates a cross section of an electrode 200. One or more ofelectrode 200 may be used in a rechargeable battery, such as thesecondary battery/cell of FIG. 1, in accordance with various embodimentsof the invention. The electrode 200 includes a substrate 210, anoptional seed layer 215, and an electrode extension 220. The electrodeextension 220 includes a support filament 230 and an intercalation layer240. The seed layer 215 may be used to initiate growth of the supportfilament 230 and to facilitate connection of the electrode extension 220to the substrate 210. In alternative embodiments the electrode extension220 is coupled directly to the substrate 210. The support filament 230supports the intercalation layer 240 and provides an electrical pathbetween the intercalation layer 240 and the substrate 210. Theintercalation layer 240 includes DAM and provides a surface/volume forintercalation of ions. The electrode 200 typically includes multipleelectrode extensions 220.

The support filament 230 is less than roughly 500 nanometers indiameter. (Averaged along its length.) More specifically, the diameterof support filament 230 may vary between 1-10 nanometers, 10-50nanometers and 100-500 nanometers.

In various embodiments, the substrate 210 includes a porous material,metal, a semiconductor, and/or an insulator. For example, the substrate210 may include a low oxygen content copper. The substrate 210 may befabricated in a variety of shapes. For example, the substrate 210 may beplanar (single sided and double sided), cylindrical, finned, and/or thelike. In some embodiments, the shape of the substrate 210 is selected soas to maximize available surface area. In various embodiments, thethickness of the substrate 210 ranges from 1 micron to 100 microns; from100 microns to a millimeter; from one millimeter to 3 millimeters, orlarger, depending on the particular application of the secondarybattery/cell 100.

The optional seed layer 215 serves one or more of a number of functionsand may include several sub-layers. For example, the seed layer 215 maycomprise an initial layer 250, an intermediate layer, and/or a finallayer 260. The seed layer 215 may be configured to control a diameter ofthe support filament 230 (defined in FIG. 3 as support filament diameter310) by controlling an area in which initial growth of the supportfilament 230 occurs. The relative and/or absolute thicknesses of theinitial layer 250, an intermediate layer, and/or a final layer 260 canbe selected to control the area of initial growth of the supportfilament 230 and thus the support filament diameter 310. The supportfilament diameter 310 is alternatively controlled use a reverse-micelleprocess wherein the diameter 310 of the initiation sites is determinedby an appropriate size or amount of seed material used in thereverse-micelle process. Those skilled in the art of CNT/CNF/NW growthwill appreciate that other methods are also available to control thediameter of the support filament 230. In some embodiments, the seedlayer 215 may control adhesion of the support filament 230 to thesubstrate. The spacing between adjacent support filaments 230 and/or thediameter of the support filaments may limit the possible thickness ofthe DAM in the intercalation layer 240, and vice-versa.

The seed layer 215 may control a density of initiation points and/or anareal density of growth initiation points for the support filament 230.The density of initiation points determines the density of supportfilament 230 attachment points. The density of attachment points may bybetween 10⁶/cm² to 10¹¹/cm², generally 10⁷/cm² to 10¹⁰/cm². Theinitiation density may be expressed as a number of support filamentinitiation sites per unit area, e.g., number/cm². The areal density isthe density of support filament 230 tips that are distal from seed layer215 and substrate 210. The areal density can be greater than the densityof attachment points because the support filaments 230 may be branched,as discussed further elsewhere herein. The areal density may beexpressed as a number of support filament tips per unit area, e.g.,number/cm².

In some embodiments, the seed layer 215 is a single material depositedon the substrate 210 in a single layer. Alternatively, the seed layer215 includes multiple (2, 3 or more) sub-layers of differing materials,e.g., initial layer 250, intermediate layer, and/or final layer 260.Each of the sub-layers of the seed layer 215 may be configured toperform various functions. For example, one of the sub-layers mayinclude a barrier layer configured to prevent migration of atoms betweenlayers; include an adhesion layer configured to bind two layerstogether; a protection layer configured to protect underlying oroverlying layers from chemical/physical degradation; a conduction layerconfigured to provide conductivity; a stress/strain layer configured toact as a mechanical buffer between two layers; a binding/release layerconfigured to bind/release the final seed material to/from theunderlying substrate; a layer configured to inhibit the growth ofCNT/CNF/NW, and/or a seed layer to initiate CNT/CNF or NW growth.Persons having ordinary skill in the art of thin film growth anddeposition will recognize that there other utilities a thin film layeredstructure of seed layer 215 can serve.

FIG. 2B is a cross section illustrating details of the seed layer 215 ofFIG. 2A, according to various embodiments of the invention. The seedlayer 215 illustrated in FIG. 2B includes a stack of sub-layerscomprising different materials. As described elsewhere herein, thesub-layers include, for example, an initial layer 250, an intermediatelayer 255 and a final layer 260. The initial layer 250 is coupled to thesubstrate and forms a base for the intermediate layer 255. Theintermediate layer 255 is deposited on the initial layer 250 andconfigured to form a base for the final layer 260. The final layer 260is deposited on the intermediate layer 255 and is configured to providesites for attachment and initiation of growth of the support filament230. Alternatively, the final layer 260 is configured to inhibit thegrowth of CNT/CNF/NW.

In various embodiments, the final layer 260 includes molybdenum, iron,cobalt, nickel and/or the like. Various materials in the final layer 260may initiate or inhibit growth and/or provide for attachment of theincluding CNT, CNF, and/or NW. The intermediate layer 255 may include,for example, iron, cobalt, nickel, titanium, titanium nitride, aluminum,and/or the like. The initial layer 250 may include, for example,platinum, tungsten, titanium, chromium, and/or the like. It will beappreciated that alternative materials may be included in the sub-layersof Seed Layer 215.

In various embodiments, the support filament 230 includes NW, CNF,and/or CNT. The support filament 230 provides a mechanical base fordeposition and growth of the intercalation layer 240. The supportfilament 230 may also provide strength (e.g., tensile strength,compression strength, shear strength, and/or the like) to the DAM of theintercalation layer 240. The additional strength reduces or preventsdamage to the intercalation layer 240 during expansion and/orcontraction of the DAM. In various embodiments, the material of thesupport filament 230 includes CNT, CNF, NW, metal, semiconductor,insulator, and/or the like. The CNT may include a single wall ormultiple walls. In some embodiments, the CNT/CNF of the support filament230 is configured to act as a DAM.

In some embodiments, the intercalation layer 240 does coat some but notall of the length of the support filament 230. As a result, a portion ofthe support filament 230 forms an uncoated trunk 235. The trunk 235 isconfigured to provide a region for flex and motion of the supportfilament 230. This flex can reduce mechanical stress resulting fromexpansion and contraction of the intercalation layer 240. If notreduced, this stress can cause breakage and/or separation of the supportfilament 230 from the seed layer 215. The length of the trunk 235 mayrange from several angstroms to several microns. In some embodiments thelength of the trunk 235 is selected such that the intercalation layer240 does not reach or only just reaches the seed layer 215 when fullyexpanded. In various embodiments the length of the trunk is at least0.1, 0.25, 0.3, 0.5, or 1.0 micrometers. In some embodiments, the lengthof the trunk 235 is substantially greater than a micron. The trunk 235is typically located proximate to the end of support filament 230closest to the seed layer 215. However, uncoated trunk 235 may beprovided at other or alternative parts of support filament 230. Forexample, uncoated trunk 235 may be provided proximate to branches withinsupport filament 230.

In some embodiments, trunk 235 is a region that has reduced coating ofintercalation layer 240 relative to other parts of electrode extension220, rather than a region having no coat at all. For example, trunk 235may have a coating of intercalation layer 240 whose thickness is lessthan 10, 25 or 50% of the thickness of the intercalation layer 240 foundin other regions of electrode extension 220.

FIG. 2C is a cross section of a portion of the electrode extension 220of FIG. 2A including an optional under-layer 290 between the supportfilament 230 and the intercalation layer 240, and an optional over-layer295 that encapsulates the intercalation layer 240. In some embodiments,the under-layer 290 is configured to provide a seed layer forvapor-liquid-solid (VLS) growth of the intercalation layer 240.Alternatively, the under-layer 290 includes a thin layer (less than onemicrometer) of a metal or a series of metals (e.g., gold, silver,copper, and/or the like) or a salt (e.g., LiF). Other materials may beused to form an under-layer 290 depending on the desired effect.

The over-layer 295 may be grown/deposited on the intercalation layer240. The over-layer 295 may partially or fully encapsulate theintercalation layer 240. The materials that comprise the over-layer 295include, for example, metals such as gold, silver, copper, and/or thelike. The over-layer 295 can also include a diamond-like coating (DLC),or an insulator, such as SiO₂, a binder, a polymer, or the like. Thethickness of the over-layer 295 is typically less than one micrometer inthe case of metals, semiconductors or insulators. In variousembodiments, the thickness of the over-layer 295 may be as large as amicrometer for a binder or larger for polymers.

The DAM may be grown/deposited on the support filament 230 using avarious methods. These methods include, for example, evaporation,sputtering, PECVD (Plasma-Enhanced Chemical Vapor Deposition),low-pressure chemical vapor deposition (LPCVD), VLS (Vapor Liquid Solidsynthesis), electroplating, electro-less deposition, “field-free”chemical vapor deposition (CVD), metal-organic CVD, molecular beamepitaxy (MBE), and/or the like. In some embodiments, the DAMdistribution over the surface of the support filament is uniform.Alternatively, the DAM distribution is not uniform over the length ofthe support filament 230. For example, the trunk 450 height may varyfrom 0% to 99% of the height of the CNT/CNF/NW. In some embodiments, theDAM proximate to the substrate 210 has a smaller thickness relative tothe distal end of the support filament 230. As such, the thickness ofthe DAM may increase, along support filament 230, with distance from thesubstrate 210.

The expansion of the DAM is dependent on the materials included in theDAM. For example, in the case of silicon the expansion may be as much400% For Sn (tin) the expansion may be roughly 233%. Cathodes expansionoccurs on insertion of the electrode into electrolyte, and when thebattery is driven to overdisharge. The thickness of a DAM can range fromseveral nanometers to several tens of microns. For example, in variousembodiments, the thickness (unexpanded) is between 1-10 nanometers,10-1000 nanometers, 1 micrometer to 50 microns. Larger thicknesses areoptionally used on a cathode relative to an anode.

A number of methods may be employed to achieve a desired length for thetrunk 235. Examples of such methods include controlling the aspect ratioof the support filaments 230 during growth, directional deposition,electro-deposition, electro-less deposition at the bottom layer toisolate the trunk, sputter and light etch of a masking layer to open thesupport filament 230 to intercalation layer 240 growth/deposition,pre-coupling layer isolation (i.e. mask seed locations) prior to growthof the support filament 230, modifying growth parameters of the supportfilament 230 to achieve an advantageous aspect ratio (such as a treelike structure), or performing a deposition and directional etch back tofree the support filament 230 from coverage by the DAM.

FIG. 3 is a cross section of the electrode 200 illustrating details ofthe support filament 230 of FIG. 2A. FIG. 3 differs from FIG. 2A in thatthe intercalation layer 240 is omitted for clarity. In variousembodiments, the support filament diameter 310 is less than 10nanometers, between 10 and 100 nanometers, between 100 and 500nanometers, and greater than 500 nanometers. The support filamentdiameter 310 may vary along the length of the support filament 230.

In various embodiments, a height 320 of the support filament 230 isabout one micron to about 100 microns, 100 microns to 500 microns, 500microns to about 1000 microns, or greater than about 1000. This heightmay vary as support filament 230 tilts or bends. An initiation site 330for the growth of support filament 230 may include a seeded base where afinal layer 260 remains attached to the preceding layer of the seedlayer after growth of the support filament 230 is complete. Optionally,the support filament 230 includes a filament extension tip 340 where thefinal layer separates from the rest of the seed layer and resides on thetip of the support filament after growth is complete.

FIG. 4A illustrates a cross section of electrode 400, according tovarious embodiments of the invention. The electrode 400 includes anelectrode extension 420 which is an alternative embodiment of theelectrode extension 220 of FIG. 2A. FIG. 4A differs from FIG. 2A in thatthe electrode extension 420 illustrated in FIG. 4A includes one or morebranches. Specifically, the electrode extension 420 includes a supportfilament 430, which includes multiple branches 420 a, 420 b, and 420 cwhich share a single trunk 450 at a single point contact to the seedlayer 215. The electrode extension 420 further includes an intercalationlayer 440 which may be applied to the support filament 430, includingthe branches 420 a-420 c. Support filament 430 and intercalation layer440 are alternative embodiments of support filament 230 andintercalation layer 240. The multiple branches 420 a-420 c illustratedin FIG. 4A provide an increase in the effective surface area of theelectrode extension 420 and, thus, an increase in the effective volumeof the DAM in the intercalation layer 440 and the surface volume of theelectrode 400. The electrode 400 may include multiple electrodeextensions 420. The electrode may include a mixture of multipleelectrode extensions 220 and 420.

FIG. 4B illustrates a cross section of alternative embodiments ofelectrode 400. The electrode 400 includes an electrode extension 425.FIG. 4B differs from FIG. 4A in that the intercalation layer 440 of theelectrode extension 425 includes intercalation branches 445 formed bythe DAM. Typically the branching structure of the intercalation branches445 are at a 0-10 nanometer scale. However, in some embodiments, thesizes of branching structure may be greater than ten nanometers.Similarly, the DAM may form branches in the intercalation layer 240 ofthe electrode extension 220, as illustrated in elsewhere herein. Theelectrode 400 optionally includes multiple electrode extensions 425. Theelectrode 400 may include a mixture of multiple electrode extensions220, 420, and/or 425.

FIG. 4C is a cross section illustrating details of the support filament430 of FIG. 4A. FIG. 4C differs from FIG. 4A and 4B in that theintercalation layer 440 is omitted for clarity. FIG. 4C differs fromFIG. 3 in that the support filament 430 illustrated in FIG. 4C includesone or more branches 430 a-430 c whereas the support filament 230illustrated in FIG. 3 does not include branches. The support filamentbranches 430 a-430 c may be generated using a variety of methods. Forexample, in one method support filament branches 430 a, 430 b, and 430 care generated by changing reactant gas flow, reactant gas type, andtemperature while growth occurs. Persons having ordinary skill in theart of CNT/CNF/NW growth will appreciate that there are a other methodsof growing additional branches 430 a, 430 b, and 430 c. While supportfilament 430 is illustrated as having three support filament branches430 a-430 c, the support filament 430 may include more branches or fewerbranches.

FIG. 5A illustrates a cross section of an electrode 500, according tovarious embodiments of the invention. Electrode 500 is an alternativeembodiment of electrodes 200 and 400. The electrode 500 includes anextension layer 510. The extension layer 510 includes an array ofmultiple electrode extensions 520. The electrode extensions 520 include,for example, electrode extensions 220, 420, and/or 425 such as thoseillustrated in FIG. 2A, 4A and 4B respectively. The electrode 500 mayfurther include an electrode extension 225 that has intercalationextensions, as discussed elsewhere herein.

FIG. 5B illustrates details of support filaments 230 and 430 of theelectrode 500 of FIG. 5A. FIG. 5B differs from FIG. 5A in that theintercalation layers 240 and 440 of the electrode extension 520 areomitted for clarity. The electrode extensions 520 as illustrated in FIG.5A and FIG. 5B optionally include an ordered or semi-ordered ensemble ofthe support filaments 230 and/or 430, as illustrated in FIGS. 3 and 4Crespectively. The electrode extensions 520 provide an electrical path,through the support filaments 230 and/or 430, to the substrate 210.Alternatively, a higher resistance is used in various applications. Thesupport filaments 230 and/or 430 also provide a mechanical base fordeposition/growth of the DAM. The support filaments 230 and/or 430further provide strength (e.g., tensile strength, compression strength,shear strength, and/or the like) to the electrode extensions 520 forsupporting the intercalation layer 240 and 440 during expansion and/orcontraction of the DAM during intercalation and preventing breakage ofthe intercalation layer and/or separation of the electrode extensions520 from the substrate 210.

The DAM may coat some but not all of the support filament 230 and/or430. In some embodiments, most of the support filament is coated by theDAM. However, the trunk 235 of the support filament 230 and/or 430 mayremain uncoated, essentially uncoated, or minimally coated. This has theeffect of allowing the DAM in the intercalation layers 240 and/or 440 toflex and move during expansion/contraction, while reducing thelikelihood of separation of the support filaments 230 and/or 430separating from the substrate 210 at the seed layer 215. In variousembodiments, the intercalation layer covers between 90 and 99%, 75 and90%, 25 and 75%, and less than 25% of support filaments 230 and/or 430.

The thickness of the DAM in the intercalation layers 240 and/or 440 maybe determined by various features of the support filaments 230 and/or430. These features include the spacing of the nearest neighbor supportfilament or support filament spacing 530 and the diameter 310 of thesupport filament 230 and/or 430.

The DAM can be grown/deposited on the support filaments 230 and/or 430to form the intercalation layer 440 using a various methods. Thesemethods include evaporation, sputtering, PECVD, low-pressure chemicalvapor deposition (LPCVD), VLS, electroplating, and electro-lessdeposition.

Various methods may be used to achieve an appropriate height of theextension layer 510. Examples of these methods include relying on theaspect ratio of the grown support filaments 230 while performing adirectional deposition; electro-deposition or electro-less deposition atthe bottom layer to isolate the trunk; sputter and light etch of amasking layer to open the support filament 230 to DAM growth/deposition;pre-coupling layer isolation (i.e. mask seed locations) prior to growthof the support filaments 230 and/or 430; modifying growth parameters ofthe support filaments 230 and/or 430 to achieve an advantageous aspectratio (such as a tree like structure), or performing a deposit anddirectional etch back to free the support filaments 230 and/or 430 fromDAM coverage.

In some embodiments, the diameter 310 of the initial growth of thesupport filament 230 and/or 430 is determined by the thickness of thefinal layer of the seed layer 215. For example, in various embodiments,the thickness of the seed layer 215 is less than 150 angstroms, between150 and 500 angstroms, and greater than 500 angstroms. The material usedfor the final layer of the seed layer 215 may also control the initialdiameter 310 of the support filament. For example, a given thickness ofnickel may produce a support filament diameter 310 during initial growthof support filaments 230 and/or 430 that is substantially different fromthe diameter produced by the same thickness of iron. Standardlithography techniques may be applied to print an initiation site 330 ofpredetermined diameter in the final layer 260 of the seed layer 215,which in turn controls the diameter 310 during initiation of growth ofthe support filament 230 and/or 430.

An initiation density 540 of extension layer 510 may be expressed interms of initiation sites per unit area. The initiation density 540depends on an average of the support filament spacing 530. An arealdensity 560 of extension layer 510 may be expressed in terms of tips 550per unit area. The areal density 560 depends on the initiation densityand average number of tips 550 per support filament 230 and/or 430. Theinitiation density 540 and the areal density 560, as well as the supportfilament spacing 530, may depend in part on the same parameters thatcontrol diameter 310. In various embodiments, the thickness of the finalseed layer, material choice, differing reverse-micelle processtechniques, a lithography pattern, and/or the like may all contribute toa determination of the initiation density 540 and/or the areal density560. In some embodiments, the support filament spacing 530 is influencedby the diameter 310 of the support filaments 230 and/or 430.

The adhesion of the support filaments 230 and/or 430 to the substrate210 is partially determined by the material choice of the seed layer,and the particular growth process employed. In some embodiments, carbidemay be formed at the base of the CNT/CNF to provide adhesion, thereforeimplying tip growth. Base growth, in some instances, may also provideadhesion.

FIG. 6A illustrates a cross section of an embodiment of electrodeextension 220 of FIG. 2A taken along line a-a. The DAM is illustrated inFIG. 6A forming a layer around the support filament 230. FIG. 6Billustrates a cross section of an embodiment of the electrode extension220 of FIG. 2A taken along line a-a. FIG. 6B differs from FIG. 6A inthat the intercalation layer 240 of FIG. 6B includes DAM protrusions 610produced using the various methods of forming nanostructures discussedelsewhere herein. The DAM process includes a base 620 and a tip 630. Abase separation 640 is a distance between the DAM bases 620 of adjacentDAM processes 610. A tip separation 650 is a distance between the DAMtips 620 of adjacent DAM processes 610. A minimum distance for a DAMbase separation 640 is about zero.

FIG. 6C illustrates a cross section of an embodiment of the electrodeextension 220 of FIG. 2A taken along line a-a. FIG. 6C differs from FIG.6A in that the electrode extension 220 includes branches 670, similar tobranches 430 a-430 c illustrated in FIG. 4B. The branches 670 include anintercalation layer 240. The intercalation layer 240 optionally does notcover the entire branch 670. Thus a branch trunk 660 is formed along thebranch 670 between the intercalation layer 240 and the support filament230. In some embodiments a branch tip separation distance 655 isdetermined by a thickness selected for the intercalation layer 240 and abranch base separation distance 645 is determined by an expansion of theintercalation layer 440 and a diameter of the branch 670.

FIG. 7 illustrates further embodiments of a support filament, accordingto various embodiments of the invention. These embodiments include asupport cap 710 and a support collar 720. Support cap 710 and supportcollar provide additional surface area to which intercalation layer 240may be attached. Support collar 720 may be disposed near the initiationcite (optionally in contact with seed layer 215), or anywhere along thelength of support filament 230 or a branch thereof.

In some embodiments the width of support cap 710 and/or support collar720 are selected to be at least as large as the width of theintercalation layer 240 when the intercalation layer is fully expanded.For example, if the intercalation layer has a diameter of 160 nanometerswhen fully expanded, then the support cap 710 and/or support collar 720are at least 160 nanometers.

In various embodiments, the support cap 710 and/or support collar 720may act as anchor points for the DAM as well as constraints for theexpansion of the DAM along the length of the electrode extension 425.For example the support cap 710 may be configured to prevent the DAMfrom moving off of the end of the support filament 430 as the result ofrepeated expansions and contractions. Support cap 710 and/or supportcollar 720 are examples of variation in the diameter of support filament430. Other variations are possible. For example, the diameter may bechanged on a periodic basis, gradually, and/or abruptly. In someembodiments, support filament 430 has a greater diameter distal from thesubstrate 210 relative to adjacent to the substrate 210.

FIG. 8 illustrates methods of producing and optionally using anelectrode, according to various embodiments of the invention. In areceive conductive substrate step 810 substrate 210 is received.Substrate 210 may be prepared for addition of seed layer 215 or directattachment of support filament 230. Substrate 210 may be provided by athird party or may be manufactured by the party performing the methodsof FIG. 8.

In an optionally form seed layer step 815, seed layer 215 is formed onsubstrate 210. Form seed layer step 815 is optional in embodimentswherein support filament 230 is attached directly to substrate 210. Insome embodiments, form seed layer step 815 includes depositing orgrowing more than one sub-layer of seed layer 215.

In a form support filaments step 820 a plurality of support filaments230 are formed on seed layer 215 or substrate 210. In variousembodiments the formed support filaments 230 have an aspect ratio(length/width) of at least 5:1, 10:1, 20:1, 50:1 or 100:1.

In a coat step 825 the support filaments 230 formed in form supportfilaments step 820 are coated with intercalation layer 240 to form anelectrode. As discussed elsewhere herein, a trunk 235 of supportfilaments 230 is optionally left uncoated or with a coat of smallerthickness than other areas of support filaments 230. In variousembodiments, the intercalation layer 240 coated on support filaments 230has at least a two, five or ten times greater ion adsorbing or absorbingcapacity for ions than the support filaments 230.

In an optional electrolyte step 830 the electrode formed in step 825 isplaced in an electrolyte solution. The electrode may be a cathode or ananode. In some embodiments, placement of the coated support filaments230 in contact with an electrolyte will cause ion uptake and swelling ofthe intercalation layer 240.

In an optional battery step 835, the electrode formed in step 825 isplaced in one cell of a rechargeable battery. The electrode may be usedas a cathode or anode. In some embodiments electrodes formed using step825 are used in both the cathode and anode of the rechargeable battery.

In an optional cycle battery step 840, the battery of step 835 isrepeatedly cycled (charged and discharged). In the process theintercalation layer 240 absorbs and desorbs ions repeatedly withoutdetaching the plurality of support filaments 230 from the substrate 210.It has been found that a rechargeable batter using some embodiments ofthe improved electrodes described herein can be fully cycled over 600times without significant loss of charge carrying capacity. This abilityto cycle can be dependent on the presence or size of trunk 235. Thisability to make repeated cycles may be achieved while at the same timeachieving an improvement in charge capacity of over six times relativeto systems that lack intercalation layer 440.

Several embodiments are specifically illustrated and/or describedherein. However, it will be appreciated that modifications andvariations are covered by the above teachings and within the scope ofthe appended claims without departing from the spirit and intended scopethereof. For example, an additional binder layer may be used to coverthe electrode including electrode extensions 220. This binder layer mayinclude an ion permeable membrane configured to pass ions to and fromintercalation layer 240.

The embodiments discussed herein are illustrative of the presentinvention. As these embodiments of the present invention are describedwith reference to illustrations, various modifications or adaptations ofthe methods and/or specific structures described may become apparent tothose skilled in the art. All such modifications, adaptations, orvariations that rely upon the teachings of the present invention, andthrough which these teachings have advanced the art, are considered tobe within the spirit and scope of the present invention. Hence, thesedescriptions and drawings should not be considered in a limiting sense,as it is understood that the present invention is in no way limited toonly the embodiments illustrated.

What is claimed is:
 1. A system comprising: A first electrode disposedin a first region of electrolyte and including a substrate, a pluralityof support filaments attached to the substrate, and a conformal ionabsorbing material attached to the support filaments and configured toexpand in volume at least 5 percent up to approximately 400 percent whenabsorbing ions; a separator configured to separate the first region anda second region of electrolyte; and a second electrode disposed in thesecond region of electrolyte, the first and second electrodes andseparator configured to operate as a rechargeable battery.
 2. The systemof claim 1, wherein the ion absorbing material covers some but not allof each of the plurality of support filaments.
 3. The system of claim 1,wherein the ion absorbing material covers an area of a member of theplurality of support filaments distal to the substrate and does notcover an area of the member of the plurality of support filamentsproximate to the substrate.
 4. The system of claim 1, wherein athickness of the ion absorbing material is greater at an end of thesupport filaments distal to the substrate relative to a thickness at anend of the support filaments proximate to the substrate.
 5. The systemof claim 1, wherein the plurality of support filaments are eachbranched.
 6. The system of claim 1, wherein the ion absorbing materialincludes silicon.
 7. The system of claim 1, wherein the plurality ofsupport filaments comprise a carbon nano-tube (CNT), a carbon nano-fiber(CNF), or a nano-wire (NW).
 8. The system of claim 1, wherein a densityof the plurality of support filaments is selected such that the ionabsorbing material can expand at least 5 percent up to approximately 400percent in volume without detaching members of the plurality of supportfilaments from the substrate.
 9. The system of claim 1, wherein theplurality of support filaments are each less than 500 nanometers andgreater than 100 nanometers in diameter.
 10. The system of claim 1further comprising an over-layer disposed over the ion absorbing layer.11. The system of claim 10 wherein the over-layer comprises silicondioxide.
 12. An electrode comprising: a conductive substrate; aplurality of support filaments attached to the substrate, the supportfilaments comprising a carbon nano-tube (CNT), a carbon nano-fiber(CNF), or a nano-wire (NW), and a conformal ion absorbing materialattached to some but not all of each of the support filaments andconfigured to expand in volume by at least five percent up toapproximately 400% when absorbing ions.
 13. The electrode of claim 12,wherein the ion absorbing material is disposed on the support filamentsso as to form a trunk of the support filaments essentially not coated bythe ion absorbing material.
 14. The electrode of claim 13, wherein thetrunk is at least 0.25 micrometers to several micrometers in length. 15.The electrode of claim 12, wherein the ion absorbing material includessilicon.
 16. The electrode of claim 12, wherein the plurality of supportfilaments are attached to the conductive substrate using a seed layer.17. The electrode of claim 16 wherein the seed layer comprises aplurality of different sub-layers.
 18. The electrode of claim 17 whereinthe plurality of different sub-layers includes a layer of a transitionmetal.
 19. The electrode of claim 12 wherein the substrate comprises aporous material.
 20. The electrode of claim 12 wherein the substratecomprises low oxygen content copper.
 21. The electrode of claim 12further comprising an over-layer disposed over the ion absorbing layer.22. The electrode of claim 21 wherein the over-layer comprises silicondioxide.
 23. A method comprising: receiving a conductive substrate;forming a plurality of support filaments coupled to the conductivesubstrate, the support filaments having an aspect ratio (length/width)of at least 10:1 to approximately 100:1; and coating the plurality ofsupport filaments with a conformal ion absorbing material to create anelectrode, the ion absorbing material having at least a two timesgreater ion absorbing capacity for ions than the support filaments. 24.The method of claim 23, further comprising forming a seed layer on thesubstrate, the seed layer configured for forming the plurality ofsupport filaments.
 25. The method of claim 23, further comprisingplacing the electrode in contact with an electrolyte.
 26. The method ofclaim 23, further comprising using the electrode in a rechargeablebattery.
 27. The method of claim 23, further comprising repeatedly usingthe electrode to absorb and desorb ions without detaching the pluralityof support filaments from the substrate.
 28. The method of claim 23,wherein coating the plurality of support filaments with the ionabsorbing material includes producing a trunk of the support filamentsproximate to the substrate essentially free of ion absorbing material.29. The method of claim 28, wherein producing the trunk comprisesforming the ion absorbing material over the entire length of eachsupport filament, masking the support filaments except where the trunkwill be produced, and exposing the support filaments to an etch toremove the ion absorbing material where exposed by the mask.
 30. Themethod of claim 23, wherein forming the plurality of support filamentsincludes vapor deposition of the support filaments.
 31. The method ofclaim 23, wherein forming the plurality of support filaments includeselectro-chemical deposition from solution of the support filaments.